Method and apparatus for obtaining geometrical data relating to a canal

ABSTRACT

The invention uses light to determine the distance from the tip of a probe to the internal wall of the canal, and based on the position of the probe, this information is used to generate information about the shape of the canal. Light with a first and a second wavelength range is directed onto a semi-transparent mirror surface at the distal portion of the probe. Light in the first wavelength range is reflected from the mirror surface to illuminate a circumferential area of the internal surface of the canal, and light in the second wavelength range is transmitted through the mirror surface to illuminate an area in front of the distal portion of the probe. The received light is analyzed in the first wavelength range to determine the distance from the probe to the internal surface of the canal at points of the circumference, and analyzed in the second wavelength range to determine the distance from the probe to an object in front of the probe. Thereby it is ensured, that the bottom surface of the canal is not touched or injured while the internal surface of the canal is measured.

AREA OF THE INVENTION

[0001] The invention relates to a method and an apparatus for obtaininggeometrical data relating to the internal surface of a canal. The methodand the apparatus are used to gain a data mapping of the internalsurface of a canal, so that a 3-dimensional data or digital model of theinternal surface of the canal is obtained. In some cases it is importantto also obtain information about a bottom surface of the canal. This isespecially important when the canal forms part of the human body. Inthis case the bottom surface may be sensitive, and should not betouched. Also in connection with inspection and measurement of othercanals, which are sensitive to contact such as surfaces of newly paintedor otherwise surface treated holes the invention may be used andprovides an advantage over the prior art.

[0002] If the human ear is mapped using the method, the 3-dimensionmodel can be used to produce a shell, which has the exact shape of theear canal and the shell may form the basis for a ITE or CIC hearing aidor an earmould for use with a BTE hearing aid. Also earmould or shellsfor other purposes such as hearing protection, or for headsets may beproduced from the data model. The shell can be produced on the basis ofthe data model in different ways, such as by recent developed rapidprototyping methods or by well known machining, e.g. in a CNC machiningcenter.

[0003] Today hearing aid shells are produced on the basis of an earimpression taken by introducing a semi-fluent material into the earcanal, which is left to cure in the ear. After curing the semi-fluentmaterial becomes elastic and coherent and is pulled out of the ear canalin one piece. A shell is produced on the basis of this ear impression.Having the ear impression taken is associated with discomfort for thepatient, and in many cases the resulting shell does not fit the canalvery well. Therefor a method and a device is sought whereby a hearingaid shell may be produced without the necessity of taking the earimpression.

[0004] The advantage of having a data model of the ear canal is that theproduction of the shell can take place at any location, which means thathearing aid manufactures may produce the shells at a central productionfacility. Uniform quality can then be ensured. Further the data modelmay be transmitted either as it is obtained or right thereafter forevaluation at a production facility. Thereby a data model of the hearingaid, which may be realized based on the geometry and shape of the canalmay be generated. The date model of the hearing aid may be transmittedback to the end user for visual evaluation.

BACKGROUND OF THE INVENTION

[0005] In the following documents some of the above problems areaddressed, but no satisfactory solutions are presented.

[0006] U.S. Pat. No. 5,487,012 discloses a method for computercontrolled production of an adaptive earpiece comprising at least onepart, which is individually matched to the contours of an auditorycanal. The method comprise the steps of tracing of the contours of theauditory canal to obtain contour data, digitization of the contour dataand storage of the digitized values, converting the digitized valuesinto a multi-dimensional computer model of the external contours of theadaptive earpiece and producing the earpiece on the basis of thecomputer model. The patent mentions that the tracing of the internalcontours of the ear canal may be performed using ultra sound. Thedocument further discloses a method for tracking the ear canal based onthe use of an ear impression, but such a method would not resolve theproblems relating to the usual way of producing shells as describedabove.

[0007] U.S. Pat. No. 5,056,204. In this document a method for producinga hearing aid, which is worn in the ear is described. The methodcomprise the steps of initially taking measurements of the inner spaceof the ear op to the eardrum for use in producing an individual shape ofthe body member corresponding with the measurements of the inner spaceof the ear. It is mentioned that the measurement is done by means of alaser. How this actually takes place is not disclosed. PCT applicationWO 00/34739 discloses a method for manufacture of a hearing aid shellcomprising a motor actuated ultrasonic probe used to acquire the shapedata of the ear canal, an image processing computer, which alsoincorporates the driving electronics for the probe, with an edgedetection algorithm used to filter the data. Thereby a digital imagefile of the three-dimensional topography of the ear canal is obtained.The ultrasonic probe is combined with a fiber optic probe used tomonitor the position of the probe within the canal. The fiber opticprobe comprises an inner coherent bundle of fibres and an objective lensthat relay the image of the canal to a CCD camera and an outerincoherent bundle of fibres that surround the coherent bundle andpermits the illumination of the canal by an external light source thatis optically coupled to the other end of the incoherent bundle. Theposition of the probe is determined solely by monitoring thedisplacement of the probe in one linear direction. Only the possibilityof monitoring the motor, which is a step-motor is mentioned for thispurpose. The probe is mounted on a stiff rod, and is not capable offollowing the possible bends of the ear canal. This limits the use ofthe probe, as many people especially older people have ear canals withsharp bends.

[0008] Various methods and apparatuses for determining the internalproperties of internal surfaces have been suggested, however none ofthese are useful when it comes to mapping the internal surface of acanal of the human body, in order to generate a digital model of theinterior wall of the canal.

[0009] U.S. Pat. No. 5,004,339 discloses an apparatus for determining acharacteristic of the inside surface of a bore comprising:

[0010] a guided wave fiber optic element capable of insertion into abore;

[0011] a laser light source for directing light onto the proximal end ofsaid fiber optic element;

[0012] means for directing light emanating from the distal end of saidfiber optic element onto the inside surface of said bore and fordirecting light reflected from the inside surface of said bore onto thedistal end of said fiber optic element; and

[0013] photo detector means capable of generating an output signaldependent upon light incident thereon;

[0014] means for directing light emanating from the proximal end of saidfiber optic element onto said photo detector means whereby the outputsignal of said photo detector provides an indication of a characteristicof an inside surface of a bore. The patent further concerns a method fordetermining a characteristic of the inside surface of a bore using theabove apparatus. The method may be employed on a body passage. Obtainingdimensional information concerning a cylindrical surface is mentioned,but not described in detail. Visualization of the bore wall of a sampleis described. The sampled and held output of array video data is fed tothe y and z axis of a storage video display with the x axis comprised bya pickoff of the movement along the bore length. No system forgenerating precise information concerning the position and orientationof the distal end of the fiber optic element is mentioned. The means fordirecting light from the distal end of the optic element onto the insidesurface of the bore may be a mirror surface or a lens such as awide-angle lens. The mirror surface can be designed to focus light on apoint of the bore wall surface which is axially forward of theforwardmost portion of the mirror. This may be used to examine thebottommost portion of a blind bore. The patent does not mention thecombined use of a mirror surface and a lens. Also the use of asemitransparent mirror intended to direct part of the light to thecircumferential surface and another part of the light to the surfacewhich is axially forward of the mirror is not mentioned.

[0015] U.S. Pat. No. 5,469,245 relates to a method and an apparatus formeasuring a three-dimensional position of a surface of a lengthwiseobject such as a pipe having a uniform cross section from acorresponding two-dimensional observed image of the object surface tomeasure, for example, the size of a defect in the surface. The patentdoes not mention systems to determine the exact location and orientationof a probe, which is inserted into the pipe.

[0016] U.S. Pat. No. 5,895,927 relates to a method an apparatus forprofiling and dimensionalizing an interior cross-sectional portion of atubular structure. The probe utilizes a disc of unfocused light toilluminate a cross-section of the interior surface and images theilluminated cross-section from the interior surface to a photo detectorarray, where the image can be evaluated. The photo detector arrayprovides a continuous video signal, which can be fed to a video monitorand to a frame grabber. The resulting array of numbers can be processedby a computer program to find those pixels, which represent theilluminated cross-section, and through this, dimensional (diameter) datamay be obtained. The patent does not mention systems for determining theposition and orientation of the probe, in order to gain informationrelating to the length of the tubular structure or relating to possiblebends in the tubular structure.

[0017] U.S. Pat. No. 6,073,043. This document describes a method andapparatus for determining the position and orientation of a remoteobject relative to a reference coordinate frame. The method andapparatus includes a plurality of field-generating elements forgenerating electromagnetic fields and a drive for applying signals tothe generating elements. The signals generate a plurality ofelectromagnetic fields that are distinguishable from one another. Theapparatus comprises a remote sensor having one or more field-sensingelements for sensing the fields generated and a processor for processingthe outputs of the sensing element(s) into remote object position andorientation relative to the generating element reference coordinateframe. The position and orientation solution is based on the exactformulation of the magnetic field coupling. The system can be used forlocating the end of a catheter or endoscope, digitizing objects forcomputer databases, virtual reality and motion tracking.

SUMMARY OF THE INVENTION

[0018] The object of the invention is to provide a method for obtaininggeometrical data relating to the internal surface of a canal in order tobe able to generate an exact model of the internal surface of the canal.It is an important aspect of the present invention, that during themeasurement a bottom wall of the canal is not touched. This is achievedby the method according to claim 1. The invention uses light todetermine the distance from the tip of a probe to the internal wall ofthe canal, and based on the position of the probe, this information isused to generate information about the shape of the canal. Light with afirst and a second wavelength range is directed onto a partiallyreflective and partially transparent surface at the distal portion ofthe probe. Light in the first wavelength range is reflected from thesurface to illuminate at least one point of a circumferential area ofthe internal surface of the canal, and light in the second wavelengthrange is transmitted through the surface to illuminate an area in frontof the distal portion of the probe. The light reflected from theilluminated areas is received and directed to at least one lightsensitive element to generate an output relating to the first and thesecond wavelength range. The output relating to the first wavelengthrange is analyzed to determine the distance from the probe to theinternal surface of the canal at points of the circumference, and theoutput relating to the second wavelength range is analyzed to determinethe distance from the probe to an object in front of the probe. Therebyit is ensured that the bottom surface of the canal is not touched orinjured while the internal surface of the canal is measured. By the useof light to determine the distance between the probe and the surface ofthe canal, it is easy to locate foreign object in the canal such as hairor earwax, and these objects are left out of the data model. In this waya more precise model is obtained. Further the use of light makes itpossible to obtain very precise data, without touching any internal wallpart of the canal.

[0019] Preferably the light sensitive element is an array of CCDelements.

[0020] In an embodiment of the method distance data are obtained andrecorded while position data concerning the spatial position androtation of the distal portion of the probe are obtained and recordedduring movement of the probe from a first to a second location. Therebyan operator may map a larger coherent area of the internal surface ofthe canal in an easy and straightforward way as the data are recordedduring operator controlled motion of the probe.

[0021] In a further embodiment the probe is flexible, and capable ofbending. This has the advantage that the probe is capable of assumingthe shape of the canal, which is not straight. This makes it possible toinsert and retract the probe the full length of the canal as the probecontinually assumes the shape of a bending canal. This aspect of theinvention is important, as the ear canal of especially elderly peoplemay have sharp bends, and by using the invention, the probe may becarefully maneuvered past such bends as data are recorded. This can bedone without making impressions in the tissue of the ear canal, whichmight corrupt the measurements.

[0022] Foreign objects such as earwax may corrupt the obtained date. Inan embodiment of the invention this is avoided by analyzing the light inorder to recognize such objects. This may be done by analyzing theoutput with respect to the spectral composition of the light received atthe light sensitive element.

[0023] Measurements may be performed while moving the probe eithertowards or away from the bottom wall of the canal. In an embodimentaccording to the invention the measurements are performed while movingthe probe away from the bottom of the canal. The operator may then placethe probe deep in the canal, while taking care that the bottom wall isnot touched, and then start the measurements and pull the probe gentlyout of the canal while taking the measurements. The probe may either bepulled out by hand, or a guiding mechanism may be provided, to make surethat the probe is moved at a uniform speed.

[0024] In an embodiment of the invention the position data are obtainedusing transdusing means transmitting a magnetic field associated withthe distal portion of the probe and second transdusing means detectingthe magnetic field generated by the transmitter fixed relative to thehead of the patient. The use of this method of obtaining the positiondata is very precise. Further it is possible to make the measurementnoise insensitive. Also the transmitter of the magnetic field may bemade small, so that it may easily be build into the tip of the probe.

[0025] A further object of the invention is to provide an apparatus forobtaining geometrical data relating to the internal surface of a canalin order to be able to generate an exact model of the internal surfaceof the canal.

[0026] This is achieved with the apparatus according to claim 9.

[0027] Claims 10-14 contain advantageous embodiments of the apparatus.

[0028] Further advantageous embodiments of the apparatus are containedin claims 15-19

[0029] According to the invention the apparatus for obtaininggeometrical data relating to the internal surface of a canal comprises:

[0030] a probe having a rod part with a proximal portion and a distalportion and comprising at least one light guide and a light source atthe proximal end of the light guide,

[0031] a light emitting distal portion insertable into the canal andhaving means for directing light containing wavelengths within a firstwavelength range and a second wavelength range from the distal end ofthe light guide onto a surface, whereby

[0032] the surface is arranged to reflect light in the first wavelengthrange onto at least one point of a circumferential area of the internalsurface of the canal, and arranged to transmit light in the secondwavelength range to illuminate the area in front of the probe,

[0033] means for receiving the light reflected from the illuminatedareas, and means for directing the received light to at least one lightsensitive element to generate an output,

[0034] means for analyzing the output relating to the first and thesecond wavelength range to determine the distance from the probe to theinternal surface of the canal at points of the circumference, and todetermine the distance to objects in front of the probe.

[0035] By using the semi-transparent mirror to simultaneously directlight towards both the circumference and the bottom wall of the canaland analyzing the reflected light, the distance to any objects in frontof the probe may be determined. Thereby it is ensured, that the probedoes not touch the bottom wall of the canal.

[0036] Focusing means in the form of a lens may be inserted in the lightpath between the light guides and the mirror, to obtain a focused lightbeam.

[0037] Preferably the light sensitive element comprise an array ofelements such as CCD elements.

[0038] In and advantageous embodiment the light path between the secondmirror surface and the CCD element comprises an image guide between thedistal end and the proximal end of the probe, and where the lightsensitive element is arranged at the proximal end of the probe, andreceives the light emitting from the image guide. A flexible image guideis chosen, so that it may bend along with the probe to follow the bendsof the ear canal. The advantage is here that no severe spacerestrictions exists at the proximal end of the probe, and the mostsuitable light sensitive element may be chosen along with possiblelenses, without regard to size.

[0039] In and advantageous embodiment at least the first mirror surfaceis arranged on a transparent body, and comprises a coating, whichreflects light in a first wavelength range and which is transparent tolight in a second wavelength range and transmits the light in the secondwavelength range. The light in the second wavelength range is directedto the area in front of the distal portion of the probe, and the lightreflected from any objects in this area is directed through thetransparent body and guided towards the light sensitive element. By thisarrangement it becomes possible to receive two images at the lightsensitive element, one of the circumference of the ear canal, and one ofthe environment in front of the tip of the probe. The two images will bein each their wavelength range but are captured by one and the samelight sensitive element.

[0040] Preferably the CCD element is sensitive to light in both thefirst and the second wavelength range and the first or the secondsensitivity range may be selected. Thereby one and the same lightsensitive element may be used to capture the two pictures, from thecircumference and from the front of the probe.

[0041] Control of the light received at the CCD element may be achievedby controlling the light input to the light guide. When the area infront of the probe is to be illuminated, light in the second wavelengthrange is inputted to the light guide, and when the circumference is tobe illuminated, light in the first wavelength is used. Control of thelight input to the light guide may be obtained through control of thelight source or by the use of filters.

[0042] In another embodiment the probe comprises two CCD elementssensitive to each their wavelength range, whereby a mirror having asemitransparent coating is arranged such that one of the light sensitiveelements receives the light from the circumference and the other lightsensitive element receives the light reflected from the area in front ofthe distal portion of the probe. In this case the two pictures areavailable at all times at the two light sensitive elements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043]FIG. 1 is a sectional view of a the distal end of a probe showingthe light path for determining the distance to the inside wall of acanal,

[0044]FIG. 2 is a sectional view of the probe in FIG. 1 showing thelight path for determining the distance to an object in front of thedistal portion of the probe,

[0045]FIG. 3 is a side view showing the human ear and the arrangement ofthe position sensors.

DESCRIPTION OF A PREFERRED EMBODIMENT

[0046] The probe shown in FIG. 1 has a distal light emitting portion anda rod portion 9 connecting the distal portion to a proximal part (notshown). The rod portion 9 comprises a flexible pipe 8 and a set of lightguides 3 and an image guide 1. The image guide 1 is placed centrally inthe pipe 8, and the light guides 3 are arranged between the pipe 8 andthe image guide 1. Near the tip of the probe the light guides 3 arefastened between an inner bushing 2 and an outer tube 6. An annular lens4B is arranged at the bushing 2 to capture the light emitting from thelight guides 3, in order to focus said light. The focused light beam isdirected to a first portion of a mirror 5 mounted at the tip of the tube6. The first portion of the mirror 5 has a circumferential conical planewith a top angle of 45°. Thereby the focused light beam emitted from thelens 4B will be directed in a right angel away from the longitudinalaxis of the probe, and towards a surrounding canal wall 11. The tipportion of the tube 6 is made of a transparent material, so that thelight may be transmitted freely through the tube wall at the tip.

[0047] In FIG. 1 the wall 11 is shown as an example in a first distanceat 11A near the tip of the probe and in a second distance 11B fartheraway from the tip of the probe. Light reflected from the wall at 11A ofthe canal will enter the tube 6 and be reflected from a second portionof the mirror 5 and enter a second lens 4A. From the lens 4A the lightis directed towards the surface of the image guide 1. If light isreflected from a wall part 11B farther away from the probe, it will alsobe directed towards the surface of the image guide 1, but as can be seenin the enlarged section labeled “5x” this light enters the image guide 1closer to the center thereof. The second portion of the mirror 5 has acircumferential conical plane, but with a top angle, which may differfrom 45°.

[0048] The image received on the surface of the image guide 1 istransmitted through the image guide 1, and will appear at the other endthereof. Here the image is captured by a CCD array (not shown). Thesignal from the CCD is transferred to signal processing unit for furtherprocessing in order to calculate the distance from the probe to thecanal wall. This is done by a triangulation method well known in theart.

[0049] In stead of an image guide 1, it is possible to arrange the CCDarray at the distal end of the probe, such that the reflected light iscaptured at the distal end of the probe. This is a simpler construction,but it requires a CCD element, which is small enough to be mounted atthe tip of the probe, which is going to enter the ear canal. The signalfrom the CCD element in this case is carried in the usual way by wireback to the proximal end of the probe to be analyzed as described todetermine the distance to the wall of the ear canal.

[0050] In the preferred embodiment a focused light beam is directedtowards the wall of the canal, but also unfocused light may be used. Theadvantage of using focused light is that the focused light providesbetter contrast and this result in a more precise detection of thedistance between the probe and the canal wall.

[0051] A single light guide may be used for both directing light to thetip of the probe and for transmitting the reflected light back to theCCD element. But this requires a beamsplitter, and has the disadvantageof a reduced signal to noise ratio, and therefore the separate lightguides are preferred.

[0052] In FIG. 2 the light path is shown in a second mode of operationof the probe. The mirror surface 5 is coated with a coating, which in afirst wavelength range reflects the light, but which in a secondwavelength range transmits the light. The light path of the light in thesecond wavelength range is shown in FIG. 2. Here light in the secondwavelength range emitted from the lens 4B passes through the lens 5 andis reflected from an object 12A, 12B in front of the probe. At 12A and12B the end wall of the canal is shown at two different distances fromthe probe. The end wall is the tympanic membrane in case the ear canalis scanned. The reflected light is transmitted through mirror element 5and through lens 4A and forms an image of the area in front of the probeon the surface of image guide 1. At the proximal end of the image guidethe two pictures, namely the front and the circumferential picture, areeither led to each their CCD element by the use of a furthersemitransparent mirror, or led to one and the same CCD element which ischosen so as to be selectively sensitive to the two wavelength ranges.

[0053] The semitransparent mirror surface 5 provides anotherpossibility, namely that a conventional picture is captured through thismirror. This is done by using the image guide in the same fashion as inusual endoscobes. Here light in the wavelength range in which the mirrorsurface is transparent is guided through the image guide from theproximal end thereof to the tip of the probe. Reflected light istransmitted back through the image guide and by means of a beamsplitterdirected towards the surface of a CCD. Thereby the CCD may capture anatural image of the objects in front of the probe, and such an imagecould be valuable for the person conducting an ear scan.

[0054] In FIG. 1 and 2 a coil 7 is shown at the tip of the probe. Thecoil is used to generate a magnetic field, which is picked up by sensorsshown schematically in FIG. 3. At each sensor position A, B and C two ormore sensors are located, which are designed to register the magneticfield in each their direction. Through this arrangement the exactlocation and orientation of the tip of the probe can be determined atany time. In the case shown in FIG. 3, the probe is located inside thecanal of a human ear, shown schematically in the figure. The threesensor locations are arranged in a fixed construction, which in use isheld immobilized relative to the patient's head. In the embodiment shownin FIG. 3, the fixed construction comprises a tripod, whereby each ofthe sensor positions are placed at the outer end of each of the branchesof the tripod. In use the coil 7 at the probe tip is driven at a fixedfrequency and by using a lock-in procedure, any noise coming from othermagnetic fields in the surroundings may be cancelled out from the sensorsignals.

[0055] Using a colour sensitive CCD element has the further advantagethat colour information may be used when analyzing the light reflectedfrom the surface of an ear canal. If white light is used, it is possibleto determine the relative content of red, green and blue light in thereceived signal, and thereby foreign objects such as earwax may beidentified. This is because earwax will reflect the light in otherwavelength ranges than the naked skin of the ear canal. If thesemitransparent mirror option described above is employed this willcause some restrictions as to how detailed the colour information is, asonly a limited range of wavelengths may be reflected from the mirrorsurface 5. In the generated data model any lump of earwax may be leftout, and the data for the particular surface of the ear canal may begenerated through extrapolation using the data from the surrounding wallparts.

[0056] In the described embodiment only one coil is located at the tipof the probe, and the coil is aligned with the length axis of the probe.This means that rotational movement of the probe about its length axiscannot be detected by measuring the magnetic field. It is suggestedaccording to the invention, that the probe is made rotationally rigid,so that if the proximal end of the probe is retained and prevented fromrotation about the length axis, then the distal end cannot rotateeither. In this way only 3 different position and 2 different rotationalparameters must be obtained to fully locate the probe in the canal.

[0057] In use the probe is gently inserted into the ear, and themagnetic sensors are placed in close relation to the patient's head.Placing the probe in the ear is done while objects in front of the probeare monitored as described through the semi transparent mirror. Thepicture captured this way is displayed on a monitor, so that theoperator may know when the probe is approaching the tympanic membrane.Once the region near the tympanic membrane is reached, the measurementsmay commence. This is done while retracting the probe as correspondingvalues of the distances to the canal wall and the position of the probeare recorded. The recording is continued until the probe reaches theouter regions of the outer ear.

[0058] A guiding arrangement for the probe may be located at the tripodshown in FIG. 3. A guiding arrangement may comprise two or more oppositeflat rollers between which the probe is to pass. By slightly squeezingthe probe between the rollers, rotational movement of the probe aroundthe length direction is prevented. Such a guiding mechanism may howeverbe implemented in many different ways, and it is not shown in thefigures or described in more detail.

1. A method for obtaining geometrical data relating to the internalsurface of a canal whereby a probe having a light emitting distalportion is inserted into the canal, the method further comprising thesteps of: directing light with wavelengths within a first and a secondrange onto a partially reflective and partially transparent surface atthe distal portion of the probe, reflecting light in the firstwavelength range from the surface to illuminate at least one point of acircumferential area of the internal surface of the canal, andtransmitting light in the second wavelength range through the surface toilluminate an area in front of the distal portion of the probe,receiving the light reflected from the illuminated areas, and directingthe received light to at least one light sensitive element to generatean output relating to the first and the second wavelength range,analyzing the output relating to the light in the first wavelength rangeto determine the distance from the probe to the internal surface of thecanal at points of the circumference, and analyzing the output relatingto the light in the second wavelength range to determine the distancefrom the probe to an object in front of the probe.
 2. A method asclaimed in claim 1, where distance data are obtained while position dataconcerning the spatial position and rotation of the distal portion ofthe probe are obtained during movement of the probe from a first to asecond location.
 3. A method as claimed in claim 2, where the probe isflexible and bends in correspondence to the bends of the canal duringthe movement of the probe from the first to the second location.
 4. Amethod as claimed in claim 1, where the light sensitive element comprisean array of sensitive elements such as CCD elements.
 5. A method asclaimed in claim 1, where the output is analyzed in order to identifyforeign objects on the surface of the canal.
 6. A method as claimed inclaim 1, where the probe is initially inserted to a position adjacent abottom wall of the canal and where the geometrical data are obtainedduring extraction of the probe from the canal.
 7. A method as claimed inclaim 2, where the position data are obtained using first transducingmeans associated with the probe transmitting a magnetic field, andsecond transducing means associated with the head detecting the magneticfield generated by the transmitter at the probe.
 8. A method as claimedin claim 1, where the canal is the human ear canal.
 9. An apparatus forobtaining geometric data relating to the internal surface of a canal,the apparatus comprising, a probe having a rod part with a proximalportion and a distal portion and comprising at least one light guide anda light source at the proximal end of the light guide, a light emittingdistal portion insertable into the canal and having means for directinglight containing wavelengths within a first wavelength range and asecond wavelength range from the distal end of the light guide onto asurface, whereby the surface is arranged to reflect light in the firstwavelength range onto at least one point of a circumferential area ofthe internal surface of the canal, and arranged to transmit light in thesecond wavelength range to illuminate the area in front of the probe,means for receiving the light reflected from the illuminated areas, andmeans for directing the received light to at least one light sensitiveelement to generate an output, means for analyzing the output relatingto the light in the first and in the second wavelength range todetermine the distance from the probe to the internal surface of thecanal at points of the circumference, and to determine the distance toobjects in front of the probe.
 10. An apparatus as claimed in claim 9,wherein the light sensitive element comprises an array of elements suchas CCD elements
 11. An apparatus as claimed in claim 9, wherein theapparatus is constructed to obtain and retrieve distance data duringmotion of the probe from a first location to a second location and wherethe apparatus comprises means for obtaining position data concerning thespatial position and rotation of the distal end of the probe during themotion of the probe from the first location to the second location. 12.An apparatus as claimed in claim 11, wherein means are provided forgenerating a data model of the internal surface of the canal on thebasis of the retrieved position and distance data.
 13. An apparatus asclaimed in claim 9, wherein the light source has a wavelength range andthe CCD element has a sensitivity range such that foreign objects in theear canal may be detected and identified through spectral analysis ofthe light received at the light sensitive element.
 14. An apparatus asclaimed in claim 11, where the means for obtaining position dataregarding the probe comprise transmitting means associated with thedistal portion of the probe, and receiving means arranged at fixedpositions outside the canal.
 15. An apparatus as claimed in claim 14,where the transmitting means comprise a coil generating a magneticfield, and the receiving means comprise magnetic sensitive elements suchas hall-elements.
 16. An apparatus as claimed in claim 10 where theprobe comprises first light guides for transmitting light from theproximal to the distal end of the probe and further comprises a secondmirror surface for directing the light reflected from thecircumferential surface of the canal towards the CCD element.
 17. Anapparatus as claimed in claim 16, where the light path between thesecond mirror surface and the light sensitive element further comprisean image guide between the distal end and the proximal end of the probe,and where the light sensitive element is arranged at the proximal end ofthe probe, and receives the light emitting from the image guide.
 18. Anapparatus as claimed in claim 10, where the CCD element is sensitive tolight in both the first and the second wavelength range and where thefirst or the second wavelength range may be selected.
 19. An apparatusas claimed in claim 10 where the probe comprises two CCD elementssensitive to each their wavelength range, whereby a second mirror havinga semitransparent coating is arranged such that one of the lightsensitive elements receives the light from the circumference and theother sensitive element receives the light reflected from the area infront of the distal portion of the probe.